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Esteruelas, Miguel A. - One of the best experts on this subject based on the ideXlab platform.

  • Repercussion of a 1,3-hydrogen shift in a hydride-osmium-allenylidene complex
    'American Chemical Society (ACS)', 2021
    Co-Authors: Esteruelas, Miguel A., Oñate Enrique, Paz Sonia, Vélez Andrea
    Abstract:

    An unusual 1,3-hydrogen shift from the metal center to the Cβ atom of the C3-chain of the allenylidene ligand in a hydride-osmium(II)-allenylidene complex is the beginning of several interesting transformations in the cumulene. The hydride-osmium(II)-allenylidene complex was prepared in two steps, starting from the tetrahydride dimer [(Os(H···H){κ3-P,O,P-[xant(PiPr2)2]})2(μ-Cl)2][BF4]2 (1). Complex 1 reacts with 1,1-diphenyl-2-propyn-1-ol to give the hydride-osmium(II)-alkenylcarbyne [OsHCl(≡CCH═CPh2){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (2), which yields OsHCl(═C═C═CPh2){κ3-P,O,P-[xant(PiPr2)2]} (3) by selective abstraction of the Cβ–H hydrogen atom of the alkenylcarbyne ligand with KtBuO. Complex 3 is metastable. According to results of DFT calculations, the migration of the hydride ligand to the Cβ atom of the cumulene has an activation energy too high to occur in a concerted manner. However, the migration can be catalyzed by water, alcohols, and aldehydes. The resulting alkenylcarbyne-osmium(0) intermediate is unstable and evolves into a 7:3 mixture of the hydride-osmium(II)-indenylidene OsHCl(═CIndPh){κ3-P,O,P-[xant(PiPr2)2]} (4) and the osmanaphthalene OsCl(C9H6Ph){κ3-P,O,P-[xant(PiPr2)2]} (5). Protonation of 4 with HBF4 leads to the elongated dihydrogen complex [OsCl(η2-H2)(═CIndPh){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (6), while the protonation of 5 regenerates 2. In contrast to 4, complex 6 evolves to a half-sandwich indenyl derivative, [Os(η5-IndPh)H{κ3-P,O,P-[xant(PiPr2)2]}][BF4]Cl (7). Phenylacetylene also provokes the 1,3-hydrogen shift in 3. However, it does not participate in the migration. In contrast to water, alcohols, and aldehydes, it stabilizes the resulting alkenylcarbyne to afford [Os(≡CCH═CPh2)(η2-HC≡CPh){κ3-P,O,P-[xant(PiPr2)2]}]Cl (8).Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R and project LMP148_18), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • Reactions of POP-pincer rhodium(I)-aryl complexes with small molecules: coordination flexibility of the ether diphosphine
    'Canadian Science Publishing', 2021
    Co-Authors: Curto, Sheila G., Esteruelas, Miguel A., Oñate Enrique, Heras, Laura A. De Las, Oliván Montserrat, Vélez Andrea
    Abstract:

    Reactions of the aryl complexes Rh(aryl){κ3-P,O,P-[xant(PiPr2)2]} (1; aryl = 3,5-Me2C6H3 (a), C6H5 (b), 3,5-Cl2C6H3 (c), 3-FC6H4 (d); xant(PiPr2)2 = 9,9-dimethyl-4,5-bis-(diisopropylphosphino)xanthene) with O2, CO, and MeO2CC≡CCO2Me have been performed. Under 1 atm of O2, the pentane solutions of complexes 1 afford the dinuclear peroxide derivatives [Rh(aryl){κ2-P,P-xant(PiPr2)2}]2(μ-O2)2 (2a–2d) as yellow solids. In solution, these species are unstable. In dichloromethane, at room temperature, they are transformed into the dioxygen adducts Rh(aryl)(η2-O2){κ3-P,O,P-[xant(PiPr2)2]} (3a–3d), as a result of the rupture of the double peroxide bridge and the reduction of the metal center. Complex 3b decomposes in benzene, at 50 °C, to give diphosphine oxide, phenol, and biphenyl. Complexes 1 react with CO to give the square-planar mono carbonyl derivatives Rh(aryl)(CO){κ2-P,P-[xant(PiPr2)2]} (4a–4d), which under carbon monoxide atmosphere evolve to benzoyl species Rh{C(O)aryl}(CO){κ2-P,P-[xant(PiPr2)2]} (5a–5d), resulting from the migratory insertion of CO into the Rh-aryl bond and the coordination of a second CO molecule. The transformation is reversible; under vacuum, complexes 5 regenerate the precursors 4. The addition of the activated alkyne to complexes 1b and 1d initially leads to the π-alkyne intermediates Rh(aryl){η2-C(CO2Me)≡C(CO2Me)}{κ3-P,O,P-[xant(PiPr2)2]} (6b, 6d), which evolve to the alkenyl derivatives Rh{(E)-C(CO2Me)=C(CO2Me)aryl}{κ3-P,O,P-[xant(PiPr2)2]} (7b, 7d). The diphosphine adapts its coordination mode to the stability requirements of the different complexes, coordinating cis-κ2-P,P in complexes 2, fac-κ3-P,O,P in compounds 3, trans-κ2-P,P in the mono carbonyl derivatives 4 and 5, and mer-κ3-P,O,P in products 6 and 7.Financial support from the MINECO of Spain (Project CTQ2017-82935-P (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_17R and project LMP148_18), FEDER, and the European Social Fund is acknowledged. L.A.d.l.H. thanks the MECD for her FPU contract (FPU17/04813).Peer reviewe

  • Direct C−H Borylation of Arenes Catalyzed by Saturated Hydride‐Boryl‐Iridium‐POP Complexes: Kinetic Analysis of the Elemental Steps
    'Wiley', 2020
    Co-Authors: Esteruelas, Miguel A., Oliván Montserrat, Martínez Antonio, Oñate Enrique
    Abstract:

    The saturated trihydride IrH3{κ3‐P,O,P‐[xant(PiPr2)2]} (1; xant(PiPr2)2=9,9‐dimethyl‐4,5‐bis(diisopropylphosphino)xanthene) activates the B−H bond of two molecules of pinacolborane (HBpin) to give H2, the hydride‐boryl derivatives IrH2(Bpin){κ3‐P,O,P‐[xant(PiPr2)2]} (2) and IrH(Bpin)2{κ3‐P,O,P‐[xant(PiPr2)2]} (3) in a sequential manner. Complex 3 activates a C−H bond of two molecules of benzene to form PhBpin and regenerates 2 and 1, also in a sequential manner. Thus, complexes 1, 2, and 3 define two cycles for the catalytic direct C−H borylation of arenes with HBpin, which have dihydride 2 as a common intermediate. C−H bond activation of the arenes is the rate‐determining step of both cycles, as the C−H oxidative addition to 3 is faster than to 2. The results from a kinetic study of the reactions of 1 and 2 with HBpin support a cooperative function of the hydride ligands in the B−H bond activation. The addition of the boron atom of the borane to a hydride facilitates the coordination of the B−H bond through the formation of κ1‐ and κ2‐dihydrideborate intermediates.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R, project LMP148_18, and predoctoral contract to A.M.), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • Kinetic Analysis and Sequencing of Si–H and C–H Bond Activation Reactions: Direct Silylation of Arenes Catalyzed by an Iridium-Polyhydride
    'American Chemical Society (ACS)', 2020
    Co-Authors: Esteruelas, Miguel A., Oliván Montserrat, Martínez Antonio, Oñate Enrique
    Abstract:

    The saturated trihydride IrH3{κ3-P,O,P-[xant(PiPr2)2]} (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) coordinates the Si–H bond of triethylsilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, and triphenylsilane to give the σ-complexes IrH3(η2-H-SiR3){κ2-cis-P,P-[xant(PiPr2)2]}, which evolve to the dihydride-silyl derivatives IrH2(SiR3){κ3-P,O,P-[xant(PiPr2)2]} (SiR3 = SiEt3 (2), SiMe(OSiMe3)2 (3), SiPh3 (4)) by means of the oxidative addition of the coordinated bond and the subsequent reductive elimination of H2. Complexes 2–4 activate a C–H bond of symmetrically and asymmetrically substituted arenes to form silylated arenes and to regenerate 1. This sequence of reactions defines a cycle for the catalytic direct C–H silylation of arenes. Stoichiometric isotopic experiments and the kinetic analysis of the transformations demonstrate that the C–H bond rupture is the rate-determining step of the catalysis. As a consequence, the selectivity of the silylation of substituted arenes is generally governed by ligand–substrate steric interactions.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R, project LMP148_18, and predoctoral contract to AM.), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • Reactions of an osmium(IV)-hydroxo complex with amino-boranes: Formation of boroxide derivatives
    'American Chemical Society (ACS)', 2019
    Co-Authors: Antiñolo Antonio, Esteruelas, Miguel A., García-yebra Cristina, Martín Jaime, Oñate Enrique, Ramos Alberto
    Abstract:

    The discovery of a reaction which allows preparation of boroxide complexes of platinum group metals and study of their behavior under CO atmosphere is described. The trihydride-osmium(IV)-hydroxo complex OsH3(OH){κ3-P,O,P-[xant(PiPr2)2]} (1, xant(PiPr2)2 = 4,5-bis(diisopropylphosphino)xanthene) reacts with the amino-boranes iPr(H)NBCy2 and iPr(H)NBBN to give the osmium(IV)-boroxide derivatives OsH3(OBR2){κ3-P,O,P-[xant(PiPr2)2]} (BR2 = BCy2 (2), BBN (3); BBN = 9-borabicyclo[3.5.1]nonane) and iPrNH2 as a consequence of the addition of the O–H bond of the hydroxo ligand of 1 to the B–N bond of the amino-boranes. At room temperature under CO atmosphere, complexes 2 and 3 eliminate H2 to afford the osmium(II)–boroxide compounds OsH(OBR2)(CO)2{κ2-P,P-[xant(PiPr2)2]} (BR2 = BCy2 (4), BBN (5)) bearing a κ2-P,P-coordinated ether-diphosphine. The subsequent reductive elimination of the borinic acids R2BOH needs heating and a long duration and leads to the tricarbonyl-osmium(0) derivative Os(CO)3{κ2-P,P-[xant(PiPr2)2]} (6) with the phosphorus atoms of the diphosphine lying in the equatorial plane of a pentagonal bypyramid of donor atoms around the metal center. In contrast to 2 and 3, under CO atmosphere, precursor 1 eliminates water to initially give the trans-dihydride OsH2(CO){κ3-P,O,P-[xant(PiPr2)2]} (7), which subsequently evolves to the cis-dihydride-cis-dicarbonyl derivative OsH2(CO)2{κ2-P,P-[xant(PiPr2)2]} (8) and finally into the tricarbonyl 6.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P, CTQ2016-77614-P and Red de Excelencia Consolider CTQ2016-81797-REDC), the Diputación General de Aragón (E06_17R), FEDER, and the European Social Fund is acknowledged. A.R. acknowledges a postdoctoral contract funded by the “Plan Propio de I + D + i” of the Universidad de Castilla-La Mancha.Peer reviewe

Kevin M Johnson - One of the best experts on this subject based on the ideXlab platform.

  • a phantom study comparing radial trajectories for accelerated cardiac 4d flow mri against a particle imaging velocimetry reference
    Magnetic Resonance in Medicine, 2021
    Co-Authors: Philip A Corrado, Kevin M Johnson, Rafael Medero, Christopher J Francois, Alejandro Roldanalzate, Oliver Wieben
    Abstract:

    PURPOSE Radial sampling is one method to accelerate 4D flow MRI acquisition, making feasible dual-velocity encoding (Venc) assessment of slow flow in the left ventricle (LV). Here, two radial trajectories are compared in vitro for this application: 3D radial (phase-contrast vastly undersampled isotropic projection, PC-VIPR) versus stack of stars (phase-contrast stack of stars, PC-SOS), with benchtop particle imaging velocimetry (PIV) serving as a reference standard. METHODS The study contained three steps: (1) Construction of an MRI- and PIV-compatible LV model from a healthy adult's CT images. (2) In vitro PIV using a pulsatile flow pump. (3) In vitro dual-Venc 4D flow MRI using PC-VIPR and PC-SOS (two repeat experiments). Each MR image set was retrospectively undersampled to five effective scan durations and compared with the PIV reference. The root-mean-square velocity vector difference (RMSE) between MRI and PIV images was compared, along with kinetic energy (KE) and wall shear stress (WSS). RESULTS RMSE increased as scan time decreased for both MR acquisitions. RMSE was 3% lower in PC-SOS images than PC-VIPR images in 30-min scans (3.8 vs. 3.9 cm/s) but 98% higher in 2.5-min scans (9.5 vs. 4.8 cm/s). PIV intrasession repeatability showed a RMSE of 4.4 cm/s, reflecting beat-to-beat flow variation, while MRI had intersession RMSEs of 3.8/3.5 cm/s for VIPR/SOS, respectively. Speed, KE, and WSS were overestimated voxel-wise in 30-min MRI scans relative to PIV by 0.4/0.3 cm/s, 0.2/0.1 μJ/mL, and 36/43 mPa, respectively, for VIPR/SOS. CONCLUSIONS PIV is feasible for application-specific 4D flow MRI protocol optimization. PC-VIPR is better-suited to dual-Venc LV imaging with short scan times.

  • noncontrast enhanced three dimensional 3d intracranial mr angiography using pseudocontinuous arterial spin labeling and accelerated 3d radial acquisition
    Magnetic Resonance in Medicine, 2013
    Co-Authors: Huimin Wu, Walter F. Block, Patrick A Turski, Charles A Mistretta, Kevin M Johnson
    Abstract:

    Pseudo-Continuous Arterial Spin Labeling (PCASL) can be used to generate non-contrast MR angiograms of the cerebrovascular structures. Previously described PCASL-based angiography techniques were limited to 2D projection images or relatively low-resolution 3D imaging due to long aquisition time. This work proposes a new PCASL-based 3D MRA method that uses an accelerated 3D radial acquisition technique (VIPR, spoiled gradient echo) as the readout. Benefiting from the sparsity provided by PCASL and noise-like artifacts of VIPR, this new method is able to obtain sub-millimeter 3D isotropic resolution and whole head coverage with a 8-minute scan. Intracranial angiography feasibility studies in healthy (N=5) and diseased (N=5) subjects show reduced saturation artifacts in PCASL-VIPR compared to a standard Time-of-Flight protocol. These initial results show great promise for PCASL-VIPR for static, dynamic, and vessel selective 3D intracranial angiography.

  • noncontrast enhanced three dimensional 3d intracranial mr angiography using pseudocontinuous arterial spin labeling and accelerated 3d radial acquisition
    Magnetic Resonance in Medicine, 2013
    Co-Authors: Walter F. Block, Patrick A Turski, Charles A Mistretta, Kevin M Johnson
    Abstract:

    Pseudocontinuous arterial spin labeling (PCASL) can be used to generate noncontrast magnetic resonance angiograms of the cerebrovascular structures. Previously described PCASL-based angiography techniques were limited to two-dimensional projection images or relatively low-resolution three-dimensional (3D) imaging due to long acquisition time. This work proposes a new PCASL-based 3D magnetic resonance angiography method that uses an accelerated 3D radial acquisition technique (VIPR, spoiled gradient echo) as the readout. Benefiting from the sparsity provided by PCASL and noise-like artifacts of VIPR, this new method is able to obtain submillimeter 3D isotropic resolution and whole head coverage with a 8-min scan. Intracranial angiography feasibility studies in healthy (N = 5) and diseased (N = 5) subjects show reduced saturation artifacts in PCASL-VIPR compared with a standard time-of-flight protocol. These initial results show great promise for PCASL-VIPR for static, dynamic, and vessel selective 3D intracranial angiography.

  • fast whole brain 4d contrast enhanced mr angiography with velocity encoding using undersampled radial acquisition and highly constrained projection reconstruction image quality assessment in volunteer subjects
    American Journal of Neuroradiology, 2011
    Co-Authors: W Chang, Kevin M Johnson, Julia Velikina, Howard A Rowley, C Mistretta, P A Turski
    Abstract:

    SUMMARY: We report on the image quality obtained by using fast contrast-enhanced whole-brain 4D radial MRA with 0.75-second temporal resolution, isotropic submillimeter spatial resolution, and velocity encoding (HYPRFlow). Images generated by HYPR-LR by using the velocity-encoded data as the constraining image were of diagnostic quality. In addition, we demonstrate that measurements of shear stress within the middle cerebral artery can be derived from the high-resolution 3D velocity data. AV : arteriovenous CE-VIPR : contrast-enhanced VIPR HYPR : highly constrained back-projection HYPRFlow : HYPR with phase contrast as constraint HYPR-LR : HYPR local reconstruction MCA : middle cerebral artery MIP : maximum intensity projection MRA : MR angiography PC-VIPR : phase-contrast VIPR SNR : signal intensity–to-noise ratio VIPR : vastly undersampled isotropic projection reconstruction WSS : wall shear stress

  • velocity measurements in the middle cerebral arteries of healthy volunteers using 3d radial phase contrast hyprflow comparison with transcranial doppler sonography and 2d phase contrast mr imaging
    American Journal of Neuroradiology, 2010
    Co-Authors: W Chang, Kevin M Johnson, Julia Velikina, Howard A Rowley, C Mistretta, Benjamin R Landgraf, Steven Kecskemeti, Oliver Wieben, P A Turski
    Abstract:

    BACKGROUND AND PURPOSE: We have developed PC HYPRFlow, a comprehensive MRA technique that includes a whole-brain CE dynamic series followed by PC velocity-encoding, yielding a time series of high-resolution morphologic angiograms with associated velocity information. In this study, we present velocity data acquired by using the PC component of PC HYPRFlow (PC-VIPR). MATERIALS AND METHODS: Ten healthy volunteers (6 women, 4 men) were scanned by using PC HYPRFlow and 2D-PC imaging, immediately followed by velocity measurements by using TCD. Velocity measurements were made in the M1 segments of the MCAs from the PC-VIPR, 2D-PC, and TCD examinations. RESULTS: PC-VIPR showed approximately 30% lower mean velocity compared with TCD, consistent with other comparisons of TCD with PC-MRA. The correlation with TCD was r = 0.793, and the correlation of PC-VIPR with 2D-PC was r = 0.723. CONCLUSIONS: PC-VIPR is a technique capable of acquiring high-resolution MRA of diagnostic quality with velocity data comparable with TCD and 2D-PC. The combination of velocity information and fast high-resolution whole-brain morphologic angiograms makes PC HYPRFlow an attractive alternative to current MRA methods.

Miguel A. Esteruelas - One of the best experts on this subject based on the ideXlab platform.

  • Rhodium-Mediated Dehydrogenative Borylation–Hydroborylation of Bis(alkyl)alkynes: Intermediates and Mechanism
    2019
    Co-Authors: Sheila G. Curto, Miguel A. Esteruelas, Montserrat Oliván, Enrique Oñate
    Abstract:

    Complex Rh­(Bpin)­{κ3-P,O,P-[xant­(PiPr2)2]} (Bpin = pinacolboryl; xant­(PiPr2)2 = 9,9-dimethyl-4,5-bis­(diiso­propyl­phos­phino)­xanthene) catalyzes the addition of B2pin2 to 3-hexyne and 4-octyne to give equimolecular mixtures of conjugated boryldienes and borylolefins, as a result of the addition of the B–B bond of the diborane to different molecules of alkynes and hydride transfer from one to the other. Both the dehydrogenative borylation and hydroborylation reactions form a catalytic cycle that has been deduced on the basis of stoichiometric studies. Complex Rh­(Bpin)­{κ3-P,O,P-[xant­(PiPr2)2]} promotes the dehydrogenative borylation of alkynes by means of reactions of insertion of the alkyne into the Rh–B bond, Z–E isomerization of the β-borylalkenyl ligand of the resulting Rh–alkenyl species, and Cγ–H bond activation of the alkyl substituent attached to the alkenyl Cα atom. As a consequence of the formation of boryldienes, the monohydride RhH­{κ3-P,O,P-[xant­(PiPr2)2]} is generated. The latter in a sequential manner reacts with the alkynes and the diborane to give the borylolefin hydroborylation products, via Rh–alkenyl intermediates, and regenerates the initial Rh–boryl compound. The latter also promotes stoichiometric cycles to prepare diboryl-2-olefins via allyl intermediates. In addition, the stoichiometric rhodium-mediated formation of 1-boryl-2-olefins is shown

  • Dehydrogenation of Formic Acid Promoted by a Trihydride-Hydroxo-Osmium(IV) Complex: Kinetics and Mechanism
    2018
    Co-Authors: Miguel A. Esteruelas, Cristina García-yebra, Jaime Martín, Enrique Oñate
    Abstract:

    The preparation of the hydroxo-osmium­(IV) complex OsH3(OH)­{xant­(PiPr2)2} (xant­(PiPr2)2 = 9,9-dimethyl-4,5-bis­(diisopropylphosphino)­xanthene) and its catalytic efficiency for the dehydrogenation of formic acid to H2 and CO2 are reported. The mechanism of the dehydrogenation has been unambiguously stablished by combining the kinetic analysis of the catalysis, the isolation of the intermediates and the kinetic analysis of their decomposition, and density functional theory (DFT) calculations on the rate-determining step. Under catalytic conditions, the trihydride-hydroxo complex reacts with formic acid to afford OsH3{κ1-O-(HCO2)}­{xant­(PiPr2)2}, which isomerizes into OsH3{κ1-H-(HCO2)}­{xant­(PiPr2)2} by means of the slippage of the metal center through a formate O–C–H path. The κ1-H-formate intermediate releases CO2 to give the previously reported tetrahydride OsH4{xant­(PiPr2)2}, which undergoes protonation with formic acid. The resulting OsH5 cation exists as an equilibrium mixture of the tautomers trihydride-compressed dihydride [OsH3(H···H)­{xant­(PiPr2)2}]+ and hydride-compressed dihydride–dihydrogen [OsH­(H···H)­(η2-H2)­{xant­(PiPr2)2}]+. The dissociation of H2 from the latter leads to [OsH3{xant­(PiPr2)2}]+, which coordinates HCO2– to regenerate the trihydride-(κ1-O-formate) complex and close the cycle. The release of CO2 from the κ1-H-formate intermediate is the rate-determining step of the catalysis

  • β‑Borylalkenyl Z–E Isomerization in Rhodium-Mediated Diboration of Nonfunctionalized Internal Alkynes
    2018
    Co-Authors: Sheila G. Curto, Miguel A. Esteruelas, Enrique Oñate, Montserrat Oliván, Andrea Vélez
    Abstract:

    The elemental steps for the preparation of (E)-pinBC­(Me)C­(Me)­Bpin (Bpin = pinacolboryl) by means of the anti addition of B2pin2 to 2-butyne, promoted by the boryl complex Rh­(Bpin)­{xant­(PiPr2)2} (1; xant­(PiPr2)2 = 9,9-dimethyl-4,5-bis­(diisopropylphosphino)­xanthene), have been analyzed from a kinetic point of view, and the intermediates of the process, the β-borylakenyl complexes Rh­{(Z)-C­(Me)C­(Me)­Bpin}­{xant­(PiPr2)2} (2) and Rh­{(E)-C­(Me)C­(Me)­Bpin}­{xant­(PiPr2)2} (3), have been isolated and fully characterized. The key step for the formation of the diborylalkene is the transformation of 2 into 3 as a result of the Z–E isomerization of the β-borylalkenyl group, which takes place via metallacyclopropene intermediates. The isomerization is sterically controlled, and the pincer diphosphine adapts its coordination mode to the requirements of the process happening to act as κ2-P,P. The Z–E isomerization of the β-borylalkenyl ligand of 2 is slower than the oxidative addition of the diborane to 1. As a consequence, under catalytic conditions, the formation of the syn-addition product (Z)-pinBC­(Me)C­(Me)­Bpin is favored, although the intermediate Rh­(Bpin)3{xant­(PiPr2)2} is much less stable than 2

  • Elongated σ‑Borane versus σ‑Borane in Pincer–POP–Osmium Complexes
    2017
    Co-Authors: Miguel A. Esteruelas, Israel Fernández, Cristina García-yebra, Jaime Martín, Enrique Oñate
    Abstract:

    Square pyramidal metal fragments OsHX­{κ3-P,O,P-[xant­(PiPr2)2]} (X = Cl, H; xant­(PiPr2)2 = 9,9-dimethyl-4,5-bis­(diisopropylphosphine)­xanthene) coordinate the B–H bond of boranes trans to the ligand X. As a consequence, elongated σ-borane and σ-borane pincer–POP–osmium complexes have been isolated and fully characterized. The interaction between the metal fragment and the coordinated B–H has been analyzed as a function of X, from spectroscopic, X-ray diffraction, and theoretical points of view. The dinuclear complex [(Os­(H···H)­{κ3-P,O,P-[xant­(PiPr2)2]})2(μ-Cl)2]­[BF4]2 (3) reacts with catecholborane (HBcat) and pinacolborane (HBpin) to give the elongated σ-borane derivative OsHCl­(η2-H-BR2)­{κ3-P,O,P-[xant­(PiPr2)2]} (BR2 = Bcat (4) and Bpin (5)), as well as H2, FBR2, and BF3. The elongated σ-borane character of 4 and 5 is supported by X-ray diffraction analysis and DFT-optimized structures of both compounds, which show distances between the coordinated B and H atoms of the borane in the range of 1.6–1.7 Å. AIM analysis of 4 reveals a triangular topology for the OsHB unit involving Os–B, Os–H, and B–H bond critical points and a ring critical point. In contrast to 3, the reaction of tetrahydride complex OsH4{κ3-P,O,P-[xant­(PiPr2)2]} (6) with HBcat leads to σ-borane derivative OsH2(η2-H-Bcat)­{κ3-P,O,P-[xant­(PiPr2)2]} (7), which shows a distance between the atoms of the coordinated B–H bond in the range of 1.4–1.5 Å. AIM analysis for the OsHB unit of 7 only displays Os–B and B–H bond critical points; therefore, it lacks a similar topology

  • Conclusive Evidence on the Mechanism of the Rhodium-Mediated Decyanative Borylation
    2015
    Co-Authors: Miguel A. Esteruelas, Montserrat Oliván, Andrea Vélez
    Abstract:

    The stoichiometric reactions proposed in the mechanism of the rhodium-mediated decyanative borylation have been performed and all relevant intermediates isolated and characterized including their X-ray structures. Complex RhCl­{xant­(PiPr2)2} (1, xant­(PiPr2)2 = 9,9-dimethyl-4,5-bis­(diisopropylphosphino)­xanthene) reacts with bis­(pinacolato)­diboron (B2pin2), in benzene, to give the rhodium­(III) derivative RhHCl­(Bpin)­{xant­(PiPr2)2} (4) and PhBpin. The reaction involves the oxidative addition of B2pin2 to 1 to give RhCl­(Bpin)2{xant­(PiPr2)2}, which eliminates ClBpin generating Rh­(Bpin)­{xant­(PiPr2)2} (2). The reaction of the latter with the solvent yields PhBpin and the monohydride RhH­{xant­(PiPr2)2} (6), which adds the eliminated ClBpin. Complex 4 and its catecholboryl counterpart RhHCl­(Bcat)­{xant­(PiPr2)2} (7) have also been obtained by oxidative addition of HBR2 to 1. Complex 2 is the promoter of the decyanative borylation. Thus, benzonitrile and 4-(trifluoromethyl)­benzonitrile insert into the Rh–B bond of 2 to form Rh­{C­(R-C6H4)NBpin}­{xant­(PiPr2)2} (R = H (8), p-CF3 (9)), which evolve into the aryl derivatives RhPh­{xant­(PiPr2)2} (3) and Rh­(p-CF3-C6H4)­{xant­(PiPr2)2} (10), as a result of the extrusion of CNBpin. The reactions of 3 and 10 with B2pin2 yield the arylBpin products and regenerate 2

Oñate Enrique - One of the best experts on this subject based on the ideXlab platform.

  • Repercussion of a 1,3-hydrogen shift in a hydride-osmium-allenylidene complex
    'American Chemical Society (ACS)', 2021
    Co-Authors: Esteruelas, Miguel A., Oñate Enrique, Paz Sonia, Vélez Andrea
    Abstract:

    An unusual 1,3-hydrogen shift from the metal center to the Cβ atom of the C3-chain of the allenylidene ligand in a hydride-osmium(II)-allenylidene complex is the beginning of several interesting transformations in the cumulene. The hydride-osmium(II)-allenylidene complex was prepared in two steps, starting from the tetrahydride dimer [(Os(H···H){κ3-P,O,P-[xant(PiPr2)2]})2(μ-Cl)2][BF4]2 (1). Complex 1 reacts with 1,1-diphenyl-2-propyn-1-ol to give the hydride-osmium(II)-alkenylcarbyne [OsHCl(≡CCH═CPh2){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (2), which yields OsHCl(═C═C═CPh2){κ3-P,O,P-[xant(PiPr2)2]} (3) by selective abstraction of the Cβ–H hydrogen atom of the alkenylcarbyne ligand with KtBuO. Complex 3 is metastable. According to results of DFT calculations, the migration of the hydride ligand to the Cβ atom of the cumulene has an activation energy too high to occur in a concerted manner. However, the migration can be catalyzed by water, alcohols, and aldehydes. The resulting alkenylcarbyne-osmium(0) intermediate is unstable and evolves into a 7:3 mixture of the hydride-osmium(II)-indenylidene OsHCl(═CIndPh){κ3-P,O,P-[xant(PiPr2)2]} (4) and the osmanaphthalene OsCl(C9H6Ph){κ3-P,O,P-[xant(PiPr2)2]} (5). Protonation of 4 with HBF4 leads to the elongated dihydrogen complex [OsCl(η2-H2)(═CIndPh){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (6), while the protonation of 5 regenerates 2. In contrast to 4, complex 6 evolves to a half-sandwich indenyl derivative, [Os(η5-IndPh)H{κ3-P,O,P-[xant(PiPr2)2]}][BF4]Cl (7). Phenylacetylene also provokes the 1,3-hydrogen shift in 3. However, it does not participate in the migration. In contrast to water, alcohols, and aldehydes, it stabilizes the resulting alkenylcarbyne to afford [Os(≡CCH═CPh2)(η2-HC≡CPh){κ3-P,O,P-[xant(PiPr2)2]}]Cl (8).Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R and project LMP148_18), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • Reactions of POP-pincer rhodium(I)-aryl complexes with small molecules: coordination flexibility of the ether diphosphine
    'Canadian Science Publishing', 2021
    Co-Authors: Curto, Sheila G., Esteruelas, Miguel A., Oñate Enrique, Heras, Laura A. De Las, Oliván Montserrat, Vélez Andrea
    Abstract:

    Reactions of the aryl complexes Rh(aryl){κ3-P,O,P-[xant(PiPr2)2]} (1; aryl = 3,5-Me2C6H3 (a), C6H5 (b), 3,5-Cl2C6H3 (c), 3-FC6H4 (d); xant(PiPr2)2 = 9,9-dimethyl-4,5-bis-(diisopropylphosphino)xanthene) with O2, CO, and MeO2CC≡CCO2Me have been performed. Under 1 atm of O2, the pentane solutions of complexes 1 afford the dinuclear peroxide derivatives [Rh(aryl){κ2-P,P-xant(PiPr2)2}]2(μ-O2)2 (2a–2d) as yellow solids. In solution, these species are unstable. In dichloromethane, at room temperature, they are transformed into the dioxygen adducts Rh(aryl)(η2-O2){κ3-P,O,P-[xant(PiPr2)2]} (3a–3d), as a result of the rupture of the double peroxide bridge and the reduction of the metal center. Complex 3b decomposes in benzene, at 50 °C, to give diphosphine oxide, phenol, and biphenyl. Complexes 1 react with CO to give the square-planar mono carbonyl derivatives Rh(aryl)(CO){κ2-P,P-[xant(PiPr2)2]} (4a–4d), which under carbon monoxide atmosphere evolve to benzoyl species Rh{C(O)aryl}(CO){κ2-P,P-[xant(PiPr2)2]} (5a–5d), resulting from the migratory insertion of CO into the Rh-aryl bond and the coordination of a second CO molecule. The transformation is reversible; under vacuum, complexes 5 regenerate the precursors 4. The addition of the activated alkyne to complexes 1b and 1d initially leads to the π-alkyne intermediates Rh(aryl){η2-C(CO2Me)≡C(CO2Me)}{κ3-P,O,P-[xant(PiPr2)2]} (6b, 6d), which evolve to the alkenyl derivatives Rh{(E)-C(CO2Me)=C(CO2Me)aryl}{κ3-P,O,P-[xant(PiPr2)2]} (7b, 7d). The diphosphine adapts its coordination mode to the stability requirements of the different complexes, coordinating cis-κ2-P,P in complexes 2, fac-κ3-P,O,P in compounds 3, trans-κ2-P,P in the mono carbonyl derivatives 4 and 5, and mer-κ3-P,O,P in products 6 and 7.Financial support from the MINECO of Spain (Project CTQ2017-82935-P (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_17R and project LMP148_18), FEDER, and the European Social Fund is acknowledged. L.A.d.l.H. thanks the MECD for her FPU contract (FPU17/04813).Peer reviewe

  • Kinetic Analysis and Sequencing of Si–H and C–H Bond Activation Reactions: Direct Silylation of Arenes Catalyzed by an Iridium-Polyhydride
    'American Chemical Society (ACS)', 2020
    Co-Authors: Esteruelas, Miguel A., Oliván Montserrat, Martínez Antonio, Oñate Enrique
    Abstract:

    The saturated trihydride IrH3{κ3-P,O,P-[xant(PiPr2)2]} (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) coordinates the Si–H bond of triethylsilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, and triphenylsilane to give the σ-complexes IrH3(η2-H-SiR3){κ2-cis-P,P-[xant(PiPr2)2]}, which evolve to the dihydride-silyl derivatives IrH2(SiR3){κ3-P,O,P-[xant(PiPr2)2]} (SiR3 = SiEt3 (2), SiMe(OSiMe3)2 (3), SiPh3 (4)) by means of the oxidative addition of the coordinated bond and the subsequent reductive elimination of H2. Complexes 2–4 activate a C–H bond of symmetrically and asymmetrically substituted arenes to form silylated arenes and to regenerate 1. This sequence of reactions defines a cycle for the catalytic direct C–H silylation of arenes. Stoichiometric isotopic experiments and the kinetic analysis of the transformations demonstrate that the C–H bond rupture is the rate-determining step of the catalysis. As a consequence, the selectivity of the silylation of substituted arenes is generally governed by ligand–substrate steric interactions.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R, project LMP148_18, and predoctoral contract to AM.), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • Direct C−H Borylation of Arenes Catalyzed by Saturated Hydride‐Boryl‐Iridium‐POP Complexes: Kinetic Analysis of the Elemental Steps
    'Wiley', 2020
    Co-Authors: Esteruelas, Miguel A., Oliván Montserrat, Martínez Antonio, Oñate Enrique
    Abstract:

    The saturated trihydride IrH3{κ3‐P,O,P‐[xant(PiPr2)2]} (1; xant(PiPr2)2=9,9‐dimethyl‐4,5‐bis(diisopropylphosphino)xanthene) activates the B−H bond of two molecules of pinacolborane (HBpin) to give H2, the hydride‐boryl derivatives IrH2(Bpin){κ3‐P,O,P‐[xant(PiPr2)2]} (2) and IrH(Bpin)2{κ3‐P,O,P‐[xant(PiPr2)2]} (3) in a sequential manner. Complex 3 activates a C−H bond of two molecules of benzene to form PhBpin and regenerates 2 and 1, also in a sequential manner. Thus, complexes 1, 2, and 3 define two cycles for the catalytic direct C−H borylation of arenes with HBpin, which have dihydride 2 as a common intermediate. C−H bond activation of the arenes is the rate‐determining step of both cycles, as the C−H oxidative addition to 3 is faster than to 2. The results from a kinetic study of the reactions of 1 and 2 with HBpin support a cooperative function of the hydride ligands in the B−H bond activation. The addition of the boron atom of the borane to a hydride facilitates the coordination of the B−H bond through the formation of κ1‐ and κ2‐dihydrideborate intermediates.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R, project LMP148_18, and predoctoral contract to A.M.), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • C(sp3)–Cl bond activation promoted by a POP-pincer Rhodium(I) complex
    'American Chemical Society (ACS)', 2019
    Co-Authors: Curto, Sheila G., Esteruelas, Miguel A., Heras, Laura A. De Las, Oliván Montserrat, Oñate Enrique
    Abstract:

    The complex [RhCl(κ3P,O,P-{xant(PiPr2)2})] (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates C(sp3)–Cl bonds of mono- and dichloroalkanes and catalyzes the dehalogenation of chloroalkanes and the homocoupling of benzyl chloride. Complex 1 reacts with chlorocyclohexane to give [RhHCl2(κ3P,O,P-{xant(PiPr2)2})] (2) and cyclohexene and promotes the dehalogenation of the chlorocycloalkane to cyclohexane using 2-propanol solutions of sodium formate as the reducing agent. The oxidative addition of benzyl chloride to 1 leads to [Rh(CH2Ph)Cl2(κ3P,O,P-{xant(PiPr2)2})] (4). The dehalogenation of this chloroalkane with 2-propanol solutions of sodium formate, in the presence of 1, gives toluene and 1,2-diphenylethane. The latter is selectively formed with KOH instead of sodium formate. Complex 1 also reacts with trans-1,2-dichlorocyclohexane and dichloromethane. The reaction with the former gives [RhCl3(κ3P,O,P-{xant(PiPr2)2})] (5) and cyclohexene, whereas complex 1 undergoes oxidative addition of dichloromethane to afford cis-dichloride-[Rh(CH2Cl)Cl2(κ3P,O,P-{xant(PiPr2)2})] (6a), which evolves into its trans-dichloride isomer 6b. The kinetic study of the overall process suggests that the oxidative addition is cis-concerted and the isomerization an intramolecular reaction which takes place through a σ-C–Cl intermediate with two conformations.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and Red de Excelencia Consolider CTQ2016-81797-REDC), the Diputacion General de Aragon (Group E06_17R and project LMP148_18), FEDER, and the European Social Fund is acknowledged. L.A.d.l.H. thanks the MECD for her FPU Contract (FPU17/04813).Peer reviewe

Oliván Montserrat - One of the best experts on this subject based on the ideXlab platform.

  • Reactions of POP-pincer rhodium(I)-aryl complexes with small molecules: coordination flexibility of the ether diphosphine
    'Canadian Science Publishing', 2021
    Co-Authors: Curto, Sheila G., Esteruelas, Miguel A., Oñate Enrique, Heras, Laura A. De Las, Oliván Montserrat, Vélez Andrea
    Abstract:

    Reactions of the aryl complexes Rh(aryl){κ3-P,O,P-[xant(PiPr2)2]} (1; aryl = 3,5-Me2C6H3 (a), C6H5 (b), 3,5-Cl2C6H3 (c), 3-FC6H4 (d); xant(PiPr2)2 = 9,9-dimethyl-4,5-bis-(diisopropylphosphino)xanthene) with O2, CO, and MeO2CC≡CCO2Me have been performed. Under 1 atm of O2, the pentane solutions of complexes 1 afford the dinuclear peroxide derivatives [Rh(aryl){κ2-P,P-xant(PiPr2)2}]2(μ-O2)2 (2a–2d) as yellow solids. In solution, these species are unstable. In dichloromethane, at room temperature, they are transformed into the dioxygen adducts Rh(aryl)(η2-O2){κ3-P,O,P-[xant(PiPr2)2]} (3a–3d), as a result of the rupture of the double peroxide bridge and the reduction of the metal center. Complex 3b decomposes in benzene, at 50 °C, to give diphosphine oxide, phenol, and biphenyl. Complexes 1 react with CO to give the square-planar mono carbonyl derivatives Rh(aryl)(CO){κ2-P,P-[xant(PiPr2)2]} (4a–4d), which under carbon monoxide atmosphere evolve to benzoyl species Rh{C(O)aryl}(CO){κ2-P,P-[xant(PiPr2)2]} (5a–5d), resulting from the migratory insertion of CO into the Rh-aryl bond and the coordination of a second CO molecule. The transformation is reversible; under vacuum, complexes 5 regenerate the precursors 4. The addition of the activated alkyne to complexes 1b and 1d initially leads to the π-alkyne intermediates Rh(aryl){η2-C(CO2Me)≡C(CO2Me)}{κ3-P,O,P-[xant(PiPr2)2]} (6b, 6d), which evolve to the alkenyl derivatives Rh{(E)-C(CO2Me)=C(CO2Me)aryl}{κ3-P,O,P-[xant(PiPr2)2]} (7b, 7d). The diphosphine adapts its coordination mode to the stability requirements of the different complexes, coordinating cis-κ2-P,P in complexes 2, fac-κ3-P,O,P in compounds 3, trans-κ2-P,P in the mono carbonyl derivatives 4 and 5, and mer-κ3-P,O,P in products 6 and 7.Financial support from the MINECO of Spain (Project CTQ2017-82935-P (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_17R and project LMP148_18), FEDER, and the European Social Fund is acknowledged. L.A.d.l.H. thanks the MECD for her FPU contract (FPU17/04813).Peer reviewe

  • Kinetic Analysis and Sequencing of Si–H and C–H Bond Activation Reactions: Direct Silylation of Arenes Catalyzed by an Iridium-Polyhydride
    'American Chemical Society (ACS)', 2020
    Co-Authors: Esteruelas, Miguel A., Oliván Montserrat, Martínez Antonio, Oñate Enrique
    Abstract:

    The saturated trihydride IrH3{κ3-P,O,P-[xant(PiPr2)2]} (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) coordinates the Si–H bond of triethylsilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, and triphenylsilane to give the σ-complexes IrH3(η2-H-SiR3){κ2-cis-P,P-[xant(PiPr2)2]}, which evolve to the dihydride-silyl derivatives IrH2(SiR3){κ3-P,O,P-[xant(PiPr2)2]} (SiR3 = SiEt3 (2), SiMe(OSiMe3)2 (3), SiPh3 (4)) by means of the oxidative addition of the coordinated bond and the subsequent reductive elimination of H2. Complexes 2–4 activate a C–H bond of symmetrically and asymmetrically substituted arenes to form silylated arenes and to regenerate 1. This sequence of reactions defines a cycle for the catalytic direct C–H silylation of arenes. Stoichiometric isotopic experiments and the kinetic analysis of the transformations demonstrate that the C–H bond rupture is the rate-determining step of the catalysis. As a consequence, the selectivity of the silylation of substituted arenes is generally governed by ligand–substrate steric interactions.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R, project LMP148_18, and predoctoral contract to AM.), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • Direct C−H Borylation of Arenes Catalyzed by Saturated Hydride‐Boryl‐Iridium‐POP Complexes: Kinetic Analysis of the Elemental Steps
    'Wiley', 2020
    Co-Authors: Esteruelas, Miguel A., Oliván Montserrat, Martínez Antonio, Oñate Enrique
    Abstract:

    The saturated trihydride IrH3{κ3‐P,O,P‐[xant(PiPr2)2]} (1; xant(PiPr2)2=9,9‐dimethyl‐4,5‐bis(diisopropylphosphino)xanthene) activates the B−H bond of two molecules of pinacolborane (HBpin) to give H2, the hydride‐boryl derivatives IrH2(Bpin){κ3‐P,O,P‐[xant(PiPr2)2]} (2) and IrH(Bpin)2{κ3‐P,O,P‐[xant(PiPr2)2]} (3) in a sequential manner. Complex 3 activates a C−H bond of two molecules of benzene to form PhBpin and regenerates 2 and 1, also in a sequential manner. Thus, complexes 1, 2, and 3 define two cycles for the catalytic direct C−H borylation of arenes with HBpin, which have dihydride 2 as a common intermediate. C−H bond activation of the arenes is the rate‐determining step of both cycles, as the C−H oxidative addition to 3 is faster than to 2. The results from a kinetic study of the reactions of 1 and 2 with HBpin support a cooperative function of the hydride ligands in the B−H bond activation. The addition of the boron atom of the borane to a hydride facilitates the coordination of the B−H bond through the formation of κ1‐ and κ2‐dihydrideborate intermediates.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R, project LMP148_18, and predoctoral contract to A.M.), FEDER, and the European Social Fund is acknowledged.Peer reviewe

  • C(sp3)–Cl bond activation promoted by a POP-pincer Rhodium(I) complex
    'American Chemical Society (ACS)', 2019
    Co-Authors: Curto, Sheila G., Esteruelas, Miguel A., Heras, Laura A. De Las, Oliván Montserrat, Oñate Enrique
    Abstract:

    The complex [RhCl(κ3P,O,P-{xant(PiPr2)2})] (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates C(sp3)–Cl bonds of mono- and dichloroalkanes and catalyzes the dehalogenation of chloroalkanes and the homocoupling of benzyl chloride. Complex 1 reacts with chlorocyclohexane to give [RhHCl2(κ3P,O,P-{xant(PiPr2)2})] (2) and cyclohexene and promotes the dehalogenation of the chlorocycloalkane to cyclohexane using 2-propanol solutions of sodium formate as the reducing agent. The oxidative addition of benzyl chloride to 1 leads to [Rh(CH2Ph)Cl2(κ3P,O,P-{xant(PiPr2)2})] (4). The dehalogenation of this chloroalkane with 2-propanol solutions of sodium formate, in the presence of 1, gives toluene and 1,2-diphenylethane. The latter is selectively formed with KOH instead of sodium formate. Complex 1 also reacts with trans-1,2-dichlorocyclohexane and dichloromethane. The reaction with the former gives [RhCl3(κ3P,O,P-{xant(PiPr2)2})] (5) and cyclohexene, whereas complex 1 undergoes oxidative addition of dichloromethane to afford cis-dichloride-[Rh(CH2Cl)Cl2(κ3P,O,P-{xant(PiPr2)2})] (6a), which evolves into its trans-dichloride isomer 6b. The kinetic study of the overall process suggests that the oxidative addition is cis-concerted and the isomerization an intramolecular reaction which takes place through a σ-C–Cl intermediate with two conformations.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and Red de Excelencia Consolider CTQ2016-81797-REDC), the Diputacion General de Aragon (Group E06_17R and project LMP148_18), FEDER, and the European Social Fund is acknowledged. L.A.d.l.H. thanks the MECD for her FPU Contract (FPU17/04813).Peer reviewe

  • Insertion of Diphenylacetylene into Rh-Hydride and Rh-Boryl Bonds: Influence of the Boryl on the Behavior of the ß-Borylalkenyl Ligand
    'American Chemical Society (ACS)', 2019
    Co-Authors: Curto, Sheila G., Esteruelas, Miguel A., Oliván Montserrat, Oñate Enrique
    Abstract:

    Reactions of complexes RhH{¿3-P, O, P-[xant(PiPr2)2]} (1) and Rh(Bpin){¿3-P, O, P-[xant(PiPr2)2]} (2; Bpin = pinacolboryl, xant(PiPr2)2 = 9, 9-dimethyl-4, 5-bis(diisopropylphosphino)xanthene) with diphenylacetylene have been studied. Complex 1 reacts with the alkyne to give the E-alkenyl derivative Rh{(E)-C(Ph)=CHPh}{¿3-P, O, P-[xant(PiPr2)2]} (3) as a result of the syn-addition of the Rh-H bond to the C-C triple bond. In benzene, at room temperature, complex 3 is unstable and slowly evolves into its Z-alkenyl isomer Rh{(Z)-C(Ph) =CHPh}{¿3-P, O, P-[xant(PiPr2)2]} (4), which is also unstable and undergoes an alkenyl-to-ortho-alkenylaryl transformation to afford Rh{C6H4-2-(E-CH=CHPh)}{¿3-P, O, P-[xant(PiPr2)2]} (5). The latter adds HBpin. The resulting rhodium(III) species, RhH(Bpin){C6H4-2-(E-CH=CHPh)}{¿3-P, O, P-[xant(PiPr2)2]} (6), eliminates trans-4, 4, 5, 5-tetramethyl-2-(2-styrylphenyl)-1, 3, 2-dioxaborolane and regenerates 1, closing a cycle for the hydroboration of the alkyne to the ortho-alkenyl-aryl compound. However, this cycle is not catalytic. The direct reaction of the alkyne with the borane in the presence of 1 leads to Z, E-mixtures of PhCH=C(Ph)Bpin. Diphenylacetylene also undergoes syn-addition of the Rh-B bond of 2. The Bpin group accelerates the isomerization of the alkenyl ligand. Thus, the resulting E-ß-borylalkenyl derivative Rh{(E)-C(Ph) =C(Bpin)Ph}{¿3-P, O, P-[xant(PiPr2)2]} (7) rapidly evolves into its Z-isomer Rh{(Z)-C(Ph) =C(Bpin)Ph}}{¿3-P, O, P-[xant(PiPr2)2]} (8), which also undergoes alkenyl-to-ortho-alkenylaryl transformation to give Rh{C6H4-2-[E-CH=C(Bpin)Ph]}{¿3-P, O, P-[xant(PiPr2)2]} (9). However, in contrast to 5, complex 9 is less stable than its precursor 8

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